|Orange elephant ear sponge, Plexaurella nutans.|
Copeland 1956, emend. Cavalier-Smith 1987, emend. Adl et al. 2005
The opisthokonts (paraphyletic phylum Choanozoa (conventionally assigned to the protist 'kingdom'). The opisthokonts, sometimes referred to as the 'Fungi/Metazoa group', are generally recognized as a monophyletic clade.
- Flagella 1
- History 2
- Taxonomy 3
- References 4
- External links 5
One common characteristic of opisthokonts is that flagellate cells, such as the sperm of most animals and the spores of the chytrid fungi, propel themselves with a single posterior flagellum. It is this feature that gives the group its name. In contrast, flagellate cells in other eukaryote groups propel themselves with one or more anterior flagella (see Zoospore morphological types). In some opisthokont groups, including most of the fungi, flagellate cells have been lost.
The close relationship between animals and fungi was suggested by Thomas Cavalier-Smith in 1987, who used the informal name opisthokonta (the formal name has been used for the chytrids by Copeland in 1956), and was supported by later genetic studies.
Early phylogenies placed fungi near the plants and other groups that have mitochondria with flat cristae, but this character varies. More recently, it has been said that holozoa (animals) and holomycota (fungi) are much more closely related to each other than either is to plants, because opisthokonts have a triple fusion of carbamoyl phosphate synthase, dihydroorotase, and aspartate carbamoyltransferase that is not present in plants, and plants have a fusion of thymidylate synthase and dihydrofolate reductase not present in the opisthokonts. Animals and fungi are also more closely related to amoebas than they are to plants, and plants are more closely related to the SAR supergroup of protists than they are to animals or fungi.
Cavalier-Smith and Stechmann argue that the uniciliate eukaryotes such as opisthokonts and Amoebozoa, collectively called unikonts, split off from the other biciliate eukaryotes, called bikonts, shortly after they evolved.
Opisthokonts are divided into
- Tree of Life Eukaryotes
- Copeland, H. F. (1956). The Classification of Lower Organisms. Palo Alto: Pacific Books.
- Adl, S.M. et al. (2005). The new higher level classification of eukaryotes with emphasis on the taxonomy of protists. Journal of eukaryotic microbiology 52: 399–451.
- Shalchian-Tabrizi K, Minge MA, Espelund M, et al. (2008). Aramayo R, ed. "Multigene phylogeny of choanozoa and the origin of animals". PLoS ONE 3 (5): e2098.
- Steenkamp ET, Wright J, Baldauf SL (2006). "The protistan origins of animals and fungi". Mol. Biol. Evol. 23 (1): 93–106.
- "Fungi/Metazoa group". Retrieved 2009-03-08.
- Huang, Jinling; Xu, Ying; Gogarten, Johann Peter (2005). "The presence of a haloarchaeal type tyrosyl-tRNA synthetase marks the opisthokonts as monophyletic". Molecular biology and evolution 22 (11): 2142–2146.
- Steenkamp, Emma T; Wright, Jane; Baldauf, Sandra L. (2006). "The protistan origins of animals and fungi". Molecular biology and Evolution 23 (1): 93–106.
- Parfrey, Laura Wegener; et al. (2006). "Evaluating support for the current classification of eukaryotic diversity". PLoS genetics 2 (12): e220.
- Torruella, Guifré; et al. (2012). "Phylogenetic relationships within the Opisthokonta based on phylogenomic analyses of conserved single-copy protein domains". Molecular Biology and Evolution 29 (2): 531–544.
- Steenkamp ET, Wright J, Baldauf SL. (2006). "The protistan origins of animals and fungi". Molecular Biology and Evolution 23 (1): 93–106. doi:10.1093/molbev/msj011. PMID 16151185
- Wainright PO, Hinkle G, Sogin ML, Stickel SK (April 1993). "Monophyletic origins of the metazoa: an evolutionary link with fungi". Science 260 (5106): 340–2.
- Stechmann, A.;
- Del Campo, J.; Ruiz-Trillo, I. (2013). "Environmental survey meta-analysis reveals hidden diversity among unicellular opisthokonts". Molecular Biology and Evolution.
Phylogeny based on:
- Eichinger, L.; Pachebat, J. A.; Glöckner, G.; Rajandream, M. A.; Sucgang, R.; Berriman, M.; Song, J.; Olsen, R.; et al. (2005). "Dictyostelium discoideum"The genome of the social amoeba . Nature 435 (7038): 43–57.
- Steenkamp, E. T.; Wright, J.; Baldauf, S. L. (2005). "The Protistan Origins of Animals and Fungi". Molecular Biology and Evolution 23 (1): 93–106.
One view of the great kingdoms and their stem groups.
The ichthyosl genome is >200 kilobase pairs in length and consists of several hundred linear chromosomes that share elaborate terminal-specific sequence patterns.
The ichthyosporeans have a two amino acid deletion in their elongation factor 1 α gene that is considered characteristic of fungi.
Corallochytrium seem likely to be more closely related to the fungi than to the animals on the basis of the presence of ergosterol in their membranes and being capable of synthesis of lysine via the α-aminoadipate (AAA) pathway.
The choanoflagellates have a circular mitochondrial DNA genome with long intergenic regions. This is four times as large as animal mitochondrial genomes and contains twice as many protein genes.
The paraphyletic taxon Choanozoa includes either non-animal holozoans, or non-animal, non-fungi opisthokonts.
- including chytrids (previously thought to be protists)
- including microsporidia (previously thought to be protists)
- including Hyaloraphidium (previously thought to be a green alga, now thought to be a chytrid)
- excluding oomycetes (water molds) (now thought to be stramenopiles)
- excluding labyrinthulomycetes (slime nets) (now thought to be stramenopiles)
- excluding myxomycetes (now thought to be amoebozoans)
- Fonticulida (fonticulid slime molds)
- Nucleariida or Cristidiscoidea (nucleariid amoebae)
Holomycota and Holozoa are composed of the following groups.